(1) Field of the Invention
The present invention relates to the synthesis of sound and particularly to the production of complex tones which simulate the sound produced by multiple instruments simultaneously playing the same note, i.e., "orchestra effect". More specifically, this invention is directed to circuitry for use in electronic musical instruments and especially to circuits for generating a waveform which will cause a transducer to produce an "ensemble" or "orchestra" effect in response to a frequency related command signal. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
The sound which results when a plurality of different instruments all produce the same nominal tone is known in the art as "orchestra effect". "Orchestra effect" is also sometimes referred to as "ensemble effect" or "string chorus effect". The latter term results from the fact that in a conventional piano a single key may excite several strings tuned to the same basic frequency. A similar effect will be produced by a human chorus singing the same note, by a brass group playing the same note, etc.
With respect to electronic musical instruments, i.e., electronic organs, implementation of "orchestra effect" permits the actuation of a single key on a single keyboard to result in the generation of a frequency mix which, to the listener, sounds as if a plurality of instruments all producing the same nominal tone had been played. Methods of simulating such an "orchestra effect" in electronic musical instruments are known in the art as exemplified by the disclosure of U.S. Pat. No. 4,354,415. In this patent a basic audio frequency signal is mixed with a plurality of further signals at different frequencies which have been derived from the basic signal and randomly frequency-shifted with respect thereto. The technique of U.S. Pat. No. 4,354,415 contemplates the use of parallel "bucket brigade" circuits which introduce different delays to the frequency related input signals thereto in response to control signals. The control signals for determining the time delays are derived from sub-audio or infra-audio signals which are typically on the order of a few cycles per second. Relatively complex circuitry is required to implement the method of U.S. Pat. No. 4,354,415. Further, bearing in mind that most modern electronic musical instruments are digital devices, the method of U.S. Pat. No. 4,354,415 is very difficult to implement digitally.
U.S. Pat. No. 3,978,755 discloses a digital electronic musical instrument which may be designed such that it permits the generation of an "ensemble effect" or "orchestra effect". In accordance with U.S. Pat. No. 3,978,755 the amplitude data of complex waveforms are stored, the stored information being read out under the control of an address generator. The frequency to be generated is determined by control signals applied to the address generator. These control signals are numerical values. In order to generate the "ensemble effect", the numerical control signal value is modified by a desired magnitude and the modified value is delivered as the control signal to a further address generator, simultaneously with the basic control signal being utilized in the customary manner, which controls the data to be read out of at least one further waveform memory. Implementation of this technique for producing an "orchestra effect" requires complex and expensive circuitry, particularly the use of many oscillators.